iPad 11:44 PM 1 * 68% blackboard.sc.edu + Lab 2: Plant competition - BIOL301L-... Plant Competition Worksheet.docx Plant%20Competition%20Worksheet... Plant Competition Worksheet Name:... BIOL 3011 Name Plant Competition Worksheet 1. A) [0.75 points] Give a general hypothesis for the effects of density on biomass of radishes or collards. In other words, how do you expect growth of plants in the high density treatments to compare to growth of those in the low density treatments? B) [0.75 points] Why? 2. A) [0.75 points] Give a general hypothesis for the effects of composition of plants in the pot on survival of radishes and collards. In other words, how do you expect growth of plants in monoculture pots to compare to growth of plants in pots where both species are present? You should address how each species is likely to be affected. B) [0.75 points] Why? 3. A) [0.5 points) Which species do you expect to be the superior competitor? iPad 11:44 PM 1 * 68% A blackboard.sc.edu 3. A) [0.5 points) Which species do you expect to be the superior competitor? B) [0.5 points] Why? C) [1 point] Provide one peer-reviewed citation supporting your claim in 3A, in CSE citation style format (You don't need to attach the article, just provide the citation). You and your group will take three above ground biomass measurements in a later lab to assess the effects of the two experimental factors (density and species) on growth of collards and radishes. The three measurements are: 1. Average Leaf Weight 2. Average Stem Height 3. Average Number of Leaves per Pot 4. [5 points] In the space provided below, construct two hypothetical graphs to display the expected outcome for above ground biomass (leaves and stems) in: •the intraspecific case for radishes or collards •the interspecific case for radishes and collards Remember to include all necessary labels and components on your graph (main title, axis titles and units, caption.) You currently have no data but you should be able to predict general trends in growth (think about what these plants look like) and thus give possible patterns for the data that you will collect at the end of the experiment. See the example graph on Blackboard (Competition graph example). iPad 11:44 PM 1 * 68% A blackboard.sc.edu 1 of 3 Interspecific and Intraspecific Competition One of the central questions in ecology is how important is competition among individuals of the same species (intraspecific) and among individuals of different species (interspecific) in determining the fitness of individuals in populations, and ultimately the structure of communities. One way to address this question is to grow organisms in single species groups and in mixed species groups in the laboratory, and compare their relative performance. Such laboratory experiments can allow a researcher to manipulate population density as well as environmental factors such as nutrients and light, i.e. limiting resources for which individuals compete, and to determine what impact these factors may have on the relative success of experimental populations. Today, we will initiate a competition experiment by planting radish and collard seeds in pots in the greenhouse. Plants will be watered daily and provided with a nutrient-rich soil. They will be placed in the research greenhouse and allowed to grow for six weeks, at which time we will count, weigh and measure the leaves, stems and roots to enable a comparison of how the two species fared in single-species pots (intraspecific competition) and in mixed-species pots (interspecific competition). Additionally, there will be pots with a low density (8 plants) and high density (64 plants). This exercise is an analysis of the effects of population density and competitors on the growth of individuals of two plant species. PLANT SPECIES We will use two plant species, radish (Raphinus sativa) and collard (Brassica oleraceae), as the experimental units. In the experiment, plants will be grown in monospecific (single species) pots as well as mixed species pots (1:1 ratio) to quantify the effects of intra and interspecific competition, respectively. Thus, three levels of plant species will be used in this experiment: radish alone, collard alone, and radish:collard mix. The collard seedlings are very easy to distinguish from the radish seedlings. The collards are shorter initially than the radishes and have smaller cotyledons. Also, the radishes have red stems and hairy first leaves. DENSITY The intensity of competition for limited resources is likely to increase as population density increases. To understand how population density may influence competitive interactions two levels of population density levels will be examined in this experiment. Low density pots will consist of 8 individuals per pot, while high density pots will contain 64 individuals. Each plant mixture (radish alone, collard alone, and the radish collard mix) will be planted at low and high density. Recall, the radish collard mix is a 1:1 ratio of radish:collard, thus the low density is a mix of 4 radish and 4 collard, along with 32 radish and 32 collard for the high density mix. iPad 11:44 PM 1 * 68% a blackboard.sc.edu 2 of 3 Important note: The success of this experiment depends on the ability of the investigator to implement the design in a consistent manner. If you place all of the seeds in the center of the pot, the actual density that the seedling will experience will be much greater than what the experimental design intended. Place the seeds equidistant from one another. In pots where two species are present, alternate species in your planting array. This will cause each individual of the two species to encounter individuals of the other species to the same extent. Fill your pots with dirt to the top and then use a second pot to tamp down the soil gently. Now add the seeds, being careful to space them equidistantly across the surface and to alternate species in the mixed species pots. After arranging your seeds on the surface of the soil in the pot, cover them with a thin layer (1 cm) of soil by sprinkling soil across the top. Be careful not to bury them too deeply. Be sure to label each of your pots with a tape label (see labeling scheme in Table 1). You need to be sure to include the following information on EACH pot: mix, density, replication #, and group ID. Each group should have a different color of tape, but the pots are likely to get shifted around throughout the semester, so labeling them clearly is vital to your ability to successfully complete this experiment. If you use the codes provided in Table 1, all you will need to do is add your group ID to be sure you know which pots are yours when we end the experiment. After six weeks we will terminate the experiment and collect data on the growth of the plants. They will be broken down, counted and weighed to determine which species was most successful under which treatment. EXPERIMENTAL DESIGN A factorial experiment consists of two or more factors, each with distinct values or "levels", and whose experimental units take on all possible combinations of these levels across all factors. An experiment using a factorial design allows one to examine simultaneously the effects of multiple independent variables as well as their degree of interaction i.e. dependence on one another). Therefore, in this experiment two factors, plant species and density, will be varied using a 3 x 2 factorial design In this experiment you are manipulating two variables, each with discrete levels. There are 3 levels of plant species (radish alone, collard alone, and radish:collard mix) and 2 levels of density (low and high) for a 3 x 2 design. Therefore, there are 6 possible treatment combinations. The class will be divided into 4 groups of students. Each group is responsible for planting FOUR REPLICATES of each of the 6 possible treatment combinations. THUS, EACH GROUP IS WILL PLANT 24 TOTAL POTS. The replicates from all groups will be pooled at the termination of the experiment for a larger sample size, which is always preferable to enable more rigorous statistical analysis. iPad 1 * 68% 11:44 PM a blackboard.sc.edu 3 of 3 Table 1: Experimental design and treatment combinations for plant competition. PLANT SPECIES RADISH COLLARD RADISH:COLLARD ALONE ALONE MIX Density Replicate Pot label Pot label Pot label 8 1 1R-8 1C-8 1R:C-8 2 2R-8 2C-8 2R:C-8 3 3R-8 3C-8 3R:C-8 4 4R-8 4C-8 4R:C-8 1 1R-64 1C-64 1R:C-64 2 2R-64 2C-64 2R:C-64 3 3R-64 3C-64 3R:C-64 4. 4R-64 4C-64 4R:C-64 Pot label code = replicate# plant species - density 64 Be sure to label all of your pots as indicated in Table 1, and with your group name and section number. PLANT COMPETITION LABORATORY SET UP NOTES There are a few important details about the lab set-up that must be kept in mind in order to execute a precise and rigorous experiment. 1. For all treatments be sure to space the seeds in a uniform distribution in the pots. That is, be sure to space the seeds equidistantly from one another. DO NOT PLACE SEEDS IN A CLUMP IN THE MIDDLE OF THE POT! 2. For the mixed species treatments: Be sure to alternate seed types as you plant (radish, collard, radish, collard). YOU DO NOT WANT ALL THE RADISH SEEDS ON ONE SIDE, AND ALL THE COLLARD SEEDS ON THE OTHER SIDE. 3. For all treatments: be sure to cover the seeds with approximately the same amount of soil. The seeds in all replicates should sit approximately 1 cm below the soil surface. THIS IS IMPORTANT, AS YOU WANT ALL THE SEEDS TO GERMINATE AT THE SAME TIME. 4. Be sure to label your pots with pot label code (see above), group name, and section number.
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